Machine to machine, M2M, communication over mobile and wireless networks is expected to become increasingly important in the future. Examples of possible M2M applications are almost countless e.g. in private cars for communicating service needs, in water or electricity meters for remote control and/or remote meter reading, in street-side vending machines for communicating when goods are out-of-stock or when enough coins are present to justify a visit for emptying, in taxi cars for validating credit cards, in surveillance cameras for home or corporate security purposes, in containers in a transport system etc.
An M2M device may be mounted at places with severely low accessibility in tough environments limiting occasion for battery exchanges and re-charging.
Hence, a mobile M2M device equipped with a modem for transporting data via a cellular network requires long battery lifetime, often without main power supply available. The device may rely on its own power supply, as is the normal case for asset tracking devices and sensor devices. For several types of devices, a battery is not a self-sufficient power source. To extend operation time of the device energy harvesting may be used to complement the internal battery. The energy harvesting can be based on extracting energy from ambient sources such as vibrations, solar energy and temperature gradient. However, sometimes energy cannot be continuously harvested and a device may run out of power. Today, such a device will be deemed switched off, meaning that it will be completely detached. So, when the device comes back after harvesting enough energy, there will be a signaling penalty associated with attach, followed by Packet Data Protocol, PDP context activation.
Currently, there are no intelligent power saving algorithms for M2M devices that are able to harvest their own energy. M2M devices are pre-programmed to access the network for sending or receiving data, or they are accessed in the downlink from the network. The output power of a mobile entity in a mobile communications network is determined by the base station e.g. a Node B. As a consequence, a method for power saving in a machine to machine device which is e.g. placed geographically out of range of manual service is desirable.